The recent developments of various formats of video signals and audio signals are stimulating the development of recording media, recording/reproducing devices, and monitor devices that can handle a plurality of signal formats. Such signals typically include analog and digital signals.
For example, as for the recording media, the D-VHS (DATA-Video Home System: a registered trademark of Victor Company of Japan, Limited) has been developed as a videotape capable of recording and reproducing both digital and analog signals. As for the recording/reproducing devices, videocassette recorders capable of recording and reproducing both digital and analog signals are developed for use with the D-VHS tape.
FIG. 17 is a schematic diagram showing videotape on which a digital signal and an analog signal are recorded.
In FIG. 17, a digital signal DT and an analog signal AT are alternately recorded on the videotape 700. The videotape 700 is reproduced in such a videocassette recorder as mentioned above and the reproduced signal is outputted in accordance with the signal formats recorded on the videotape.
In the field of monitor devices, too, television receivers etc. are developed for use with the videotape and videocassette recorders mentioned above.
FIG. 18 is a block diagram showing the structure of a monitor device that can process digital and analog signals.
In FIG. 18, the monitor device 400 is connected with a recording/reproducing device 800 through two cables AL and DL.
The cable AL transfers an analog signal AT outputted from the recording/reproducing device 800. The cable DL transfers a digital signal DT outputted from the recording/reproducing device 800.
The recording/reproducing device 800 is, for example, a videocassette recorder that has a function of recording/reproducing both digital and analog signals as mentioned above. When the recording/reproducing device 800 is a videocassette recorder, the recording/reproducing device 800 records the signal input from the monitor device 400 on videotape or outputs the information recorded on videotape to the monitor device 400 as a reproduction signal.
An input switch device 410, typically a remote controller, instructs the monitor device 400 to perform given operations.
The monitor device 400 includes a decoder 30, an input select device 420, an analog/digital switch device SW4, an OSD (On Screen Display) circuit 60, a video processing circuit 70, a video synthesizing circuit 71, a video output circuit 72, a video display device 73, an audio processing circuit 80, an audio output circuit 81, and an audio output device 82.
The decoder 30 has a digital terminal DP4. The reproduction signal that is sent from the recording/reproducing device 800 through the cable DL to the digital terminal DP4 is a digital signal. The decoder 30 decodes the digital signal from the digital terminal DP4 and outputs the decoded analog signal to the analog/digital switch device SW4.
The input select device 420, formed of a microcomputer, selects the signal format to be reproduced on the basis of an instruction signal from the input switch device 410, and instructs the analog/digital switch device SW4 to provide for video display and audio output in the selected signal format.
The analog/digital switch device SW4 has an analog terminal AP4 and an analog terminal DP5. The reproduction signal inputted to the analog terminal AP4 is an analog signal and the reproduction signal inputted to the analog terminal DP 5 is the analog signal decoded in the decoder 30.
On the basis of an instruction from the input select device 420, the analog/digital switch device SW4 selects the analog signal from the analog terminal AP4 or the analog signal from the analog terminal DP5 and outputs it to the video processing circuit 70 and the audio processing circuit 80.
Now, the reproduction signal (the analog signal or digital signal) includes a video signal and an audio signal; the analog/digital switch device SW4 outputs the video signal to the video processing circuit 70 and the audio signal to the audio processing circuit 80.
The OSD circuit 60 outputs a graphic signal to the video synthesizing circuit 71 to superimpose characters etc. on the image displayed on the screen of the video display device 73. The video processing circuit 70 processes in a given manner the video signal from the analog/digital switch device SW4 and outputs the video signal to the video synthesizing circuit 71.
The video synthesizing circuit 71 synthesizes the graphic signal from the OSD circuit 60 and the video signal from the video processing circuit 70 and outputs the synthesized video signal to the video output circuit 72. When the graphic signal from the OSD circuit 60 is absent, only the video signal from the video processing circuit 70 is outputted to the video output circuit 72.
The video output circuit 72 outputs the input video signal to the video display device 73. The video display device 73, including, e.g. a cathode-ray tube, liquid crystal, or plasma display, provides video display on the basis of the input video signal. The video processing circuit 70, video synthesizing circuit 71, video output circuit 72, and video display device 73 form the video display system.
The audio processing circuit 80 processes in a given way the audio signal inputted from the analog/digital switch device SW4 and outputs the audio signal to the audio output circuit 81. The audio output circuit 81 outputs the input audio signal to the audio output device 82. The audio output device 82, including a speaker etc., provides audio output on the basis of the input audio signal. The audio processing circuit 80, audio output circuit 81, and audio output device 82 form the audio output system.
When the recording/reproducing device 800 reproduces information recorded on the above-described videotape 700 in the structure shown in FIG. 18, the monitor device 400 operates as shown below.
It is assumed that the analog signal AT containing video and audio information is recorded in the first part on the videotape 700, followed by the digital signal DT containing video and audio information. It is also assumed that the monitor device 400 is set to output a reproduction signal with the analog signal AT.
First, the analog signal AT outputted from the recording/reproducing device 800 is inputted to the analog/digital switch device SW4 through the cable AL and the analog terminal AP4.
When the monitor device 400 recognizes that it should output a reproduction signal with the analog signal AT, the analog/digital switch device SW4 outputs the analog signal AT received at the analog terminal AP4 to the video display system and the audio output system. Then the analog signal AT outputted to the video display system and the audio output system is displayed as video and outputted as sound.
Next, suppose that during the reproduction of the videotape 700, the video and audio signals recorded on the videotape 700 have switched to the digital signal DT.
At this time, the recording/reproducing device 800 outputs the digital signal DT to the decoder 30 through the cable DL and the digital terminal DP4.
The digital signal DT is decoded in the decoder 30 and sent to the analog/digital switch device SW4 through the analog terminal DP5. However, receiving the analog signal decoded in the decoder 30, the analog/digital switch device SW4 does not output the decoded analog signal received at the analog terminal DP5 to the video display system and the audio output system, because, among the reproduction signal inputs, it is set to output only the analog signal AT received at the analog terminal AP4 to the video processing circuit 70 and the audio processing circuit 80.
Thus, despite the fact that the digital signal DT from the videotape 700 is providing the video signal and audio signal, the monitor device 400 is unable to perform video display and audio output operations on the basis of the digital signal DT.
Thus the information reproduced from the video and audio signals on the videotape 700 is suddenly interrupted and then the viewer of the monitor device 400 cannot obtain the reproduced information. The viewer then recognizes the condition of the monitor device 400 and notices that the video and audio information recorded on the videotape 700 has changed from the analog signal AT to the digital signal DT.
The viewer therefore operates the input switch device 410 to send to the monitor device 400 an instruction signal k1 indicating that the signal to be reproduced currently is the digital signal DT.
The instruction signal k1 is inputted to the input select device 420. Receiving the instruction signal k1, the input select device 420 recognizes that the signal to be reproduced currently is the digital signal DT and outputs an instruction signal k2 to the analog/digital switch device SW4 to cause it to output the analog signal decoded in the decoder 30 and applied to the analog terminal DP5, to the video processing circuit 70 and the audio processing circuit 80. Then the analog/digital switch device SW4 outputs the decoded analog signal to the video display system and the audio output system, and thus the video display and audio output can be made on the basis of the digital signal DT.
According to the monitor device 400 described above, the viewer who desires to obtain the signal information reproduced from the videotape 700 has to know whether the currently outputted reproduced signal is an analog signal or a digital signal. When the reproduction signal from the recording/reproducing device 800 has changed from the analog signal to the digital signal, the viewer has to take the trouble to manually switch the signal from analog to digital.
Recently, a plurality of recording/reproducing devices may be connected to a single monitor device. When the monitor device 400 shown above has a function of allowing a plurality of recording/reproducing devices to be connected thereto, the viewer has to know the signal formats of the plurality of reproduction signals outputted from the individual recording/reproducing devices in order to obtain information on the monitor device with desired ones of the reproduction signals outputted from the plurality of recording/reproducing devices.